Discovered 1771 by Charles Messier
M46 is a very rich open cluster of approximately 500 stars of which some 150 are of magnitude 13 or higher. From relatively dark sky locations, M46 is easily visible with the aid of binoculars. The cluster is relatively young with an age of about 300 million years. The cluster spans an angular diameter of about 27 minutes of arc. This is almost the size of the full Moon and at the cluster distance of approximately 5,400 lightyears equates to a diameter of about 30 lightyears. A special feature of the cluster is the planetary nebula NGC 2438 which appears below the center of the image above. This nebula is actually a foreground object with and extimated distance of about 3,000 lightyears. Planetary nebulae are formed by the final gasps of aging, and dying, Sun-like stars. They are fleeting celestial objects and most fade in a matter of a few 10s of thousands of years.
A close up view of NGC 2438 may be here.